ABB Relion 670 Series Technical Reference Manual page 819

1MRK505222-UUS C
13.5.2.2
Technical reference manual
Blocking schemes are particular favorable for three-terminal applications if there is no
zero-sequence outfeed from the tapping. The blocking scheme is immune to current
reversals because the received signal is maintained long enough to avoid unwanted
operation due to current reversal. There is never any need for weak-end infeed logic,
because the strong end trips for an internal fault when no blocking signal is received
from the weak end. The fault clearing time is however generally longer for a blocking
scheme than for a permissive scheme.
If the fault is on the line, the forward direction measuring element operates. If no
blocking signal comes from the other line end via the CR binary input (received signal)
the TRIP output is activated after the tCoord set time delay.
CS_STOP
BLOCK
PLTR_CRD
CR
0
50ms
ANSI05000448 V1 EN
Figure 402: Simplified logic diagram for blocking scheme
Permissive under/overreaching scheme
In the permissive scheme the forward directed ground-fault measuring element sends a
permissive signal to the other end, if a ground fault is detected in the forward direction.
The directional element at the other line end must wait for a permissive signal before
activating a trip signal. Independent channels must be available for the communication
in each direction.
An impedance measuring IED, which works in the same type of permissive mode, with
one channel in each direction, can share the channels with the communication scheme
for residual overcurrent protection. If the impedance measuring IED works in the
permissive overreaching mode, common channels can be used in single line
applications. In case of double lines connected to a common bus at both ends, use
common channels only if the ratio Z
impedance) is about equal at both ends. If the ratio is different, the impedance
AND
AND
0-tCoord
0
AND
/Z (positive through zero-sequence source
1S 0S
Section 13
Scheme communication
0
25ms
ANSI05000448-1-en.vsd
CS
TRIP
CRL
813